Help with RJ45 from Zebra ZT411 Printer

I need to replace multiple RJ45 ports in Zebra ZT411 thermal printers.

I bought P/N 2057-MTJ-88TX1-FSD-LG-ND as a replacement part.

I am having flickers and distortion on the touch panel of the printer with them installed. The port functions and grabs an IP but the display is very erratic.

I tore open the original RJ45 that I pulled off the board an noticed there are magnetic coils inside a chip on it. I then purchased P/N RB1-125BAG1A which has magnetics but they do not work at all.

I am at a loss at this point and would appreciate any help from more experienced techs.

I attached some pics of the original RJ45 i removed from the Zebra printer…



Hello,

Thank you for your post.

In regard to your screen not working properly, it sounds like something was either overheated or not grounded properly in the repair process. I would suggest checking you solder joints to make sure everything is seated and soldered properly.

Thanks for your response. That was my intial thought. The thing is though that I can put the original RJ45 back in and it works perfectly so the issue is most likely with me not finding the proper RJ45 that works with the printer. The display being glitchy seems to be related to noise or something else coming over the ethernet cable. The amount of the display issues changes depending on what cable I use to hook the printer up as well. When I put the original port back in it works flawlessly with any cable I use.

One should probably not assume that the phenomena are directly related. The jack is for communications; if those are working, it’s very possible that there’s a loose connector or some such causing the display issues.

That does seem to suggest a more causal link…

Anyhow, it’s useful to have an understanding of what the magnetics in an ethernet interface do. Referring to the diagram for the referenced device with internal magnetics, it can be seen that it contains 4 magnetic cores.

The two labeled with turns ratios are transformers. Each couples information onto one of the 4 twisted pairs in a cat5 cable, while preventing the transfer of DC current between the cable and the signalling circuitry within the device. That’s important, because “ground” between any two devices one might connect with an ethernet cable are not guaranteed to be at the same potential.

The other two are common-mode chokes. They act to suppress the passage of AC signals that are common to both conductors of a signal pair. That’s important because from a distance, that pair looks a lot like a big 'ol antenna, capable of transmitting or receiving all manners of ugly.

The four resistors are involved in impedance matching/termination for common-mode signals of this sort, and that 2kV (!) capacitor provides an AC-short to “ground” for such at RF frequencies while preventing too much ugly from happening in the conceivable case that AC line power shows up on the cable for some reason.

Footprint compatibility aside, I could imagine some subtle difference of internal construction giving rise to the issues described. Some sleuthing to determine what the schematic for the OEM part might look like could prove instructive–not all such devices use 1:1 transformers for example…

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